The BBC's flagship children's show Blue Peter is 40 years old - and BBC Two is hosting a special night of programmes to celebrate its birthday.

The evening sees former stalwarts Valerie Singleton, John Noakes and Peter Purves back in the Blue Peter studio for an evening of nostalgic viewing.

It will be the first time they have sat on the famous sofa in 27 years. They promise a night to trip the memories of all ages - with a phone vote to decide the best Blue Peter decade of all.

The evening kicks off with Carry On Blue Peter, in which current presenters Konnie Huq, Katy Hill, Richard Bacon and Stuart Miles introduce classic out-takes and mistakes from the decades.

It's A Dog's Life profiles the Blue Peter dogs from the days of Petra, Patch, Shep and Goldie through to today's pets, Bonnie and Mabel.

Former presenter Anthea Turner - better known now for stints on The National Lottery Live and GMTV - reveals how she used to share her bed with Bonnie, much to her husband's annoyance.

Spoofing Blue Peter

After the watershed, Spoof Peter shows how numerous comedy shows have used Blue Peter as their theme, from the Friday Night Armstice team breaking into the Blue Peter Garden, to Lily Savage's disgust at the real contents of the Blue Peter time capsule.

BP Confidential takes a serious look at how the show developed from an innocent children's programme to a lynchpin of BBC One's schedule, and the personal and professional pressures on presenters and producers.

The Princess Royal joins the line-up in A Right Royal Reunion, in which she reminisces with Valerie Singleton about her trip to Kenya for a 1971 Blue Peter special.

It was one of her first solo visits, and she returns to Africa to visit the boys' home funded by a Blue Peter appeal.

Finally, Dawn French stars in Murder At Teatime as Bunty Breslaw, a children's TV presenter driven to crime by jealousy.

Exploding myths

Throughout the night, myths about the show - such as the story of how Blue Peter's time capsule was 'lost' - will be debunked, and celebrities will be appearing to offer their own memories of the show.

The theme night is not the only celebration the BBC has planned for the programme.

Blue Peter itself will be hosting a special edition on Friday featuring a host of former presenters.

Among them will be one of the first ever presenters, Leila Williams, who now runs a pub in Tolworth, south London.

Simon Groom, Peter Duncan, Anthea Turner, John Leslie and Mark Curry will also be among the old favourites.

Blue Peter Night runs from 6pm to 7pm, and 8.55pm to 11.05pm (1700 to 1800 and 1955 to 2205 GMT) on Saturday on BBC Two.